An energy-saving tendency in household electrical appliances has been advancing more and more against global warming and environmental problems. As an example, lighting equipment has been changing from incandescent lamps of higher luminous efficacy to fluorescent tubes. For further energy saving, products in which LEDs (Light Emitting Diodes) are used as light sources have been increasing gradually. However, quite large numbers of LED chips or large-scale LED chips are used to increase the total luminous flux as a whole light source, leading to cost increases and a high expensiveness in spite of a merit that LEDs are semipermanently usable in comparison to fluorescent tubes. This makes an obstacle to wide-spreading of those LED-incorporated products.
The luminous efficacy of LEDs as it stands has been improved to as high as 100-150 lm/W, but there are problems in cost and deficiencies in total luminous flux per price as described above, necessitating further improvement in luminous efficacy. Then, reduction of optical loss is important for the improvement of luminous efficacy.
In an LED as a conventional light emitting device, for example as shown in JP 2004-356116 A, an LED chip is mounted on an insulating substrate having anode and cathode interconnect patterns formed on its one surface, and P-side and N-side electrodes formed on the surface of the LED chip are electrically connected to the anode and cathode interconnect patterns by gold wire. The LED chip is die-bonded by transparent epoxy resin or the like.
The LED chip, which emits blue light having a peak wavelength at 450 nm, is so formed that a GaN-based semiconductor layer is stacked on a sapphire substrate while the P-side electrode and the N-side electrode are formed in opposition to each other on the surface side of the chip.
A perimeter of the LED chip is sealed by a transparent resin containing a fluorophor that, upon receiving light of the LED chip, emits yellow light having a peak wavelength at a long wavelength, for example, 525 nm.